1. Field of the Invention
The present invention relates to amplifiers and in particular to a sequential RF amplifier that utilizes a single amplifier stage that amplifies the incoming signal twice in sequence before transmitting the signal to the output terminal.
2. Description of Related Art
It is well known in the prior art that particularly in handling RF signals and, under certain circumstances, with other signals having a frequency lower than RF frequencies, signal radiation within the amplifying circuit occurs such that if more than two stages of amplification at the same frequency are used, feedback can occur that prevents the circuit from operating. This is overcome in the prior art by utilizing single, double, and triple conversions or more to reduce the frequency to lower levels at each stage so that it can be amplified further without causing the previous amplifying stages or succeeding amplifying stages to oscillate.
As set forth in commonly assigned U.S. Pat. No. 5,357,206 issued Oct. 18, 1994 and entitled "Sequential Amplifier", incorporated herein by reference in its entirety, this problem in the prior art was overcome by utilizing a sequential amplifier in which first and second amplifier stages, both amplifying the same frequency, were coupled to each other by a delay line. During the time the first amplifier stage is operating and amplifying the signal and feeding it into the delay line, the second amplifier stage is turned off. Substantially at the time the amplified signal emerges from the delay line, the first amplifier stage is shut OFF by a switching unit and the second amplifier stage is turned ON. Thus there is no oscillation because only one of the amplifier stages is substantially ON at any one time. This circuit performs its function well. However, as higher frequencies are encountered, limitations begin to occur because the switching of amplifier stages ON and OFF takes time. They do not immediately turn ON or immediately turn OFF. Clearly, then, there is an upper frequency limitation at which the circuit can operate.